1. Field of Invention
The present invention relates to a suspension for use in vehicles and more particularly relates to a torsion bar-type suspension.
2. Description of Related Art
A torsion bar-type suspension has been conventionally employed as a suspension for use in vehicles. The torsion bar-type suspension includes an arm mechanism and a torsion bar spring (hereinafter referred to simply as a torsion bar). The arm mechanism supports a wheel and is vertically rotatably coupled to a vehicle body. The torsion bar is securely interposed between the arm mechanism and the vehicle body and undergoes torsional deformation in response to vertical rotation of the arm mechanism.
When a force acts on a wheel in a top-to-bottom direction with respect to the vehicle body, the arm mechanism vertically rotates. Since the torsion bar undergoes torsional deformation in response to the rotation of the arm mechanism, the top-to-bottom force acting on the wheel is damped.
When a vehicle goes over a relatively small bump on a road, a force acts on the wheel in a fore-to-aft direction with respect to the vehicle body. This force does not cause the torsion bar to be deformed. Therefore, the fore-to-aft force acting on the wheel is transmitted to the vehicle body without being damped by the torsion bar.
The fore-to-aft force transmitted to the vehicle body makes a driver feel uncomfortable. Thus, making the driver feel comfortable in driving the vehicle requires means for damping the fore-to-aft force transmitted from the torsion bar to the vehicle body.
For example, a torsion bar-type suspension equipped with such means, which is exclusively used for a front wheel of a vehicle, is disclosed in U.S. Pat. No. 3,288,487. In this suspension, the torsion bar is coupled to a cross member serving as a vehicle body frame via a floating member which is disposed behind the cross member and laterally extends in parallel therewith. The torsion bar, which penetrates the cross member to extend toward a rear part of the vehicle, is fixed to the floating member at a rear end thereof. The floating member and the cross member are coupled to each other by an elastic member.
In this construction, a fore-to-aft force acting on the wheel is transmitted from the floating member to the cross member via the elastic member. The elastic member expands and contracts, thus damping the fore-to-aft force. In this manner, the aforementioned conventional suspension provides attenuation of the fore-to-aft force acting on the vehicle body.
In general, an engine and a fuel tank are disposed across the cross member. Thus, easy installation of the engine and the fuel tank requires that a sufficiently ample space be secured across the cross member. However, in the aforementioned conventional suspension, the floating member and the elastic member occupy a space behind the cross member. Thus, the space for installation of the engine and the fuel tank is limited.
In a case where the floating member is disposed outside the cross member, the force transmitted from the floating member to the cross member is indicated by arrows in FIG. 6.
As can be seen from FIG. 6, in the case where the floating member 42 is disposed outside the cross member 36, the force acts on only one of the walls of the cross member 36. Thus, the cross section of the cross member 36 is greatly widened as indicated by a broken line in FIG. 6. In order to prevent such deformation, the cross member 36 must be provided with a reinforcement bottom plate such that the cross section thereof takes a shape of a closed box. However, this countermeasure increases the overall weight of the cross member 36.
In order to ensure that the elastic member effectively damps the fore-to-aft force acting on the wheel, the elastic member is required to exhibit a low rigidity in a direction in which it expands and contracts. On the other hand, when a force acts on the wheel in a top-to-bottom direction with respect to the vehicle body, a counterforce generated by torsional deformation of the torsion bar is applied to the elastic member as a shear force. As described above, the torsion bar-type suspension is constructed such that the top-to-bottom force acting on the wheel is damped by torsional deformation of the torsion bar. That is, the elastic member does not have to attenuate that force. Therefore, an attempt to increase durability requires that the elastic member exhibit a high rigidity in a direction in which it receives a shear force. In the aforementioned conventional suspension, it is preferable that the elastic member exhibit a high rigidity in the direction in which it expands and contracts and exhibit a low rigidity in the direction in which it receives a shear force. As a result, the overall size of the elastic member increases, whereby there is little space left behind the cross member.